Potentiometer



Sept. 12, 1961 w. A. SHERWOOD POTENTIOMETER Filed Dec. 5, 1958 2Sheets-Sheet l INVENTOR h ATTORNEY Sept. 12, 1961 W. A. SHERWOODPOTENTIOMETER 2 Sheets-:Sheet 2 Filed Dec. 5, 1958 INVENTOR W6? 0. M

MTTORNEYS United States Patent 2,999,993 POTENTIOIVIETER Walter A.Sherwood, Hempstead, N.Y., assignor, by mesne assignments, to ChandlerEvans Corporation, West Hartford, Conn., a corporation of Delaware FiledDec. 5, 1958, Ser. No. 778,522 8 Claims. (Cl. 338-176) This inventionrelates to a potentiometer and method of making same.

It is an object of the invention to provide a potentiometer of greatdurability in which the resistance element is isolated from the contactregion so that wear resulting from movement across said region of aslider or other movable contact will have little or no effect upon theresistance value, even when the contact pressure is substantial.

Another object is to provide a multiplicity of connecting elementsbetween the resistance element and the contact region, all beingcontinually in electric and thermal communication with the resistanceelement and thus aiding in the dissipation of heat therefrom.

A further object is to provide a composite resistance element in whichthe components may have, for example, opposite temperature coefiicients,and may be so disposed as to constitute a resistance element having azero temperature coeflicient over a given range.

A still further object is to provide a potentiometer in which theresistance element may be profiled or otherwise shaped and correlatedwith the shape or path of movement of the adjustable contact to obtainan output representing almost any desired function, linear or otherwise.

Another object is to provide a method of making potentiometers of thecharacter described in which only very simple apparatus is usedeffectively to make simultaneously a plurality of potentiometer unitshaving identical or differing sizes or shapes, as desired.

A further object is to provide certain improvements in the form,construction, arrangement and materials of the potentiometers, and inthe steps of the method, whereby the above named and other objects mayeffectively be attained.

Practical embodiments of the invention are represented in theaccompanying drawings, wherein:

FIG. 1 represents a perspective view of a potentiometer;

FIG.- 2 represents a detail section on the line II,II of FIG. 1, on anenlarged scale, parts being broken away;

FIG. 3 represents a more or less diagrammatic elevation of apparatussuitable for carrying out themethod,

parts being in section;

FIG. 4 represents a perspective view of the product of the apparatus ofFIG. 3, on an enlarged scale and with parts broken away, said productbeing a plurality of potentiometers in an intermediate stage ofmanufacture;

FIG. 5 represents in section a detail of an alternative form ofpotentiometer construction;

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and those adjoining it (4, 5) being covered with a resinous insulatingcoating 6. The laminated body may conveniently be provided also with endblocks 7, 8, and a suitable binding post 9 or other desired terminal isnormally connected to the resistance material 3 at each end thereof,either directly on the end blocks or through conductive clips or othermounting means. The face 10 of the laminated body is left wholly orpartially exposed for the passage thereover of a slider or other movablecontact (not shown) of any well-known or approved type.

The performance characteristics of such a potentiometer depend on theproportions of the several elements and the materials from which theyare made. The laminated body of FIGS. 1 and 2. may, for instance, have avertical thickness of /8" to A, a length from end to end of 1" to 4"(depending on the range to be covered) and a width from A3 to an inch ortwo. Each foil conductor bar 1 may have a thickness of .00025 to .0005"and each lamina of insulation may have a thickness of .0005" to .001,all said dimensions being given as examples and not as limitations. Thelayer of resistance material 3 is in electrical contact with the entirebottom edge of each conductor bar 1, said material being graphite orlamp 'black for the higher resistances or a vacuum deposited film ofmetal such as Nichrome, nickel, silver or other appropriate material forlower resistances. By judicious selection of materials on the basis oftheir known coeflicients of resistance, potentiometers havingresistances covering desired ranges within the over-all limits of about10 ohms to about 50 megohms can be provided; a convenient and commonlyrequired unit is that having a range from 50 to ohms. The resistance 3may also be composite, i.e., a carbon film having a negative temperaturecoefficient combined with a metallic film having a positive temperaturecoeflicient, to produce a resistance having a zero temperaturecoefficient over a given range.

The foil conductor bars 1 can suitably be made from such materials asaluminum, silver, Phosphor bronze and nickel. The wear resistance of thesofter materials can be improved by plating the upper edges (at the face10 of the laminated body) with chromium.

The laminations of insulating material 2 are conveniently made of paperimpregnated with an insulating adhesive, such as one of the epoxycompounds, or a Mylar (polyethylene 'terephthlate resin) film; suchmaterials are suitable for use up to temperatures of 250 F. to 300 F.but for higher temperatures glass or other inorganic materials may beneeded. Teflon (polytetrafluoroethylene) can withstand temperatures upto about 400 F. but has limited dielectric properties.

A simple form of apparatus for making potentiometers 'of the characterdescribed is shown, somewhat diagrammatically, in FIG. 3, Where supplyrolls of foil 11 and paper 12 are supported on a stand 13 with theiraxes horizontal and parallel. The winder comprises a pair of pins 14,spaced apart, lying parallel with the supply roll axes and suitablysupported so that at least one pin can be revolved around the winderaxis 15. As shown in FIG. 3 the pins 14 are equidistant from the axis 15and both revolve as indicated by the arrow 16.

The foil 11 runs straight from its supply roll to the winder, while thepaper 12 passes into a tank 17 containing liquid adhesive, under a guideroll 18 (shown as being secured resiliently to the bottom of the tank bya spring 19), then up between wipers 20 and on upward to the winder. Itwill be evident that, as the winder pins 14 are revolved around the axis15, the paper and foil looped around the pins at each end and havingparallel straight sidesspaced apartby approximately the diameter ofthepins. Whena sufiicient number of laminations have been built up, theelongated body is slipped off the pins and its sides pressed firmlytogether, as by clamping jaws 21 (FIG. 4), the pressure being continueduntil the adhesive has been" set, with or without the use of heat.The'laminated t body is then-removed from the clamps and is'cuttransversely ('e.g., sawed-n lines-22 of FIG. 4) into blocks ofapproximately the desired size, the lamination-edge faces of which-maythen be milled or ground to the proper exact'size. To'rem'ove burrswhich might'produce short circuits between laminations the blocks may bedipped into a caustic soda'b'ath (for aluminum foil) then washed innitric acid to'neutralize the soda and rinsed in water toremove the'acidand soda. By careful control of the timing, this treatment can removeall burrs and smeared edges andwill give a clean fresh surface on whichthe applied'resistance film will make excellent electrical contact withthe foil edges. After the resistance layer 3 has been applied to aselected surface all surfaces except the working surface (normallyopposite-the layer 3) are coated witha resinousinsulating compound 6.

If increased wear resistance and local hardness are required under anyspecial circumstances the edges" of the foil at the working face may beplated with chromium or the like.

According to the alternative procedure illustrated in FIGS. 5, 6 and 7,a body of insulating material 22, such as glass, has fine parallelgrooves 23- cut in one of its surfaces. A deposit of metal, such assilver, is then a'pplied'to the grooved surface, filling the grooves andcovering the lands between the grooves at least to some extent, as shownat 24-inFIG. 5. The coated surface is then ground off (FIG. 6) to adepth suflicient'to remove the coating and some of the glass,leavinga'smoothly ground surface 25 (FIG. 7) traversed by bars ofconducting material 26. A layer of resistance material 27 is applied toan adjacent surface of the insulating. body 22, making good electriccontact with theexposed ends of the conductive bars 26. An insulatingand protective covering (like the coating 6, BIG. 1) may then be appliedto all surfaces except the ground working surface 25.

In each form shown and described above, the resistance material iscompletely enclosed by a protective coating, is never toucheddirectly-by the slider or other movable contact, but is brought intoelectrical connection therewith through conductive strips touchingthe'resistancematerial at a multiplicity of' spaced points. The movablecontact travels along a smooth working. surface; where it bears on theconductive strips one by one or, preferably, with a span of about- 2 to2 /2 of such strips. The foil layers (FIGS. 1 and 2) or metal bars'(FIG: 7) are as numerous and closely spaced as possible so as tominimize the resistance difference'between adjacent layers orbars andthus-improvethe resolution. Thus, a one inch block may be made up offoil and paper layers each having a 'tliickness of .0005, or .001" perdouble layer,- so that there will be" 1000 doublelayers per inch. Suchablock can be made by operating the apparatus of FIG. 3 through 500revolutions of the jig:.bearing;.the pins 14. Thealternative-form ofFIG. 7 is particularly. suited to use with: heavier loads but'can'be'made to give ultra fine resolution bythe use of adiffraction grating(20,000 or more grooves per inch) for the-body 22.

By. varying. the size, shape and/orcompositionof the layers ofresistance material 3 or 27 the responses maybe varied as desired withstraight lineartravel of the: slider or other movable contact. Also, byvarying the rate and/ or path of travel of the pick-upmeans othervariations'in the response can be obtained. For example,-ifthe pick-upis caused to follow a circular path on the working .surface 10 or 25 itwill give a continuous sine wave output. If the pick-up traverse is anarc, the dispositionof the resistance material can be--such thatequal-angles of traverse will give equal resistance increl ments. If thelaminated unit of FIGS. 1 to 4 is mounted in, and held together by, aframe (particularly one capable of compressing the laminations) theadhesive may be omitted.

It will be understood that various changes may be made in the form,construction, arrangement and material of the several parts and in thesteps of the method without departing from the'spirit and scope of theinvention. v

What I'claim is:

l. A potentiometer comprising thin parallel strips of conductivematerial, insulating material so disposed as to separate said conductivestrips, a body of continuously conductive material lying in contact witheach of said strips, parts of said strips and said insulating. materialspaced from the resistance material lying exposed in a common plane toconstitute a smooth working-surface for the passage of suitable pick-upmeans, and a protective insulating coating covering the resistancematerial and'adjacent surfaces of the conductive strips and insulatingmaterial.

2. A potentiometer according to claim 1 in which the conductive materialis metal foil and the insulatingmaterial is in the form of thin sheetslaminated with the foil to form a multi-laminar block with the edges ofthe foil exposed on at least two faces thereof, the resistance materialbeingv applied to one of said faces in contact with each foil lamina andanother of said faces constituting the working surface.

3. A potentiometer according. to claim 1 in which the insulatingmaterial separating the conductive material is paper impregnated with aninsulating adhesive.

4. A potentiometer according to claim 1 in which the insulatingmaterial'separating the conductive material is a fusible inorganic vitreousmaterial.

5. A potentiometer according to claim 1 in which the body of resistancematerial is a vacuum deposited film of metal.

6. A potentiometer comprising thin parallel strips of conductivematerial, insulating material so disposed as to separate said conductivestrips, and a body of continuously conductive resistance material lyingin contact with each of said strips, parts of said strips and saidinsulating material spaced from the resistance material lying exposed ina common plane to constitute a smooth working surface for passage ofsuitable pick-up. means, and a protective insulating coating coveringtheresistance material and adjacent surfaces of the conductive strips andinsulating material, the strips of conductive material being'provided,at their parts along the path of travel of the pick-up means, with aconductive plating of higher wear-resistant material.

7. In a potentiometer of the character described, an elongated compositebody of continuously conductive re sistance material constituted by alayer of material havingv a negativetemperatu're coefficient and a layerof material having a positive temperature coeflicient, so associatedthat'the effective temperature coefiicient of the composite body is,throughout a desired range, a function of the'sum of -the' coefficientsof said layers.

8; A' potentiometer of the character described comprising, an elongatedbody of continuously conductive resistance material, a plurality ofstrips of conductive material each having one end in contact with theresistance material and the points of contact being'spaced along saidelongated body, insulating-means separating said strips of conductivematerial, and a Working surface spaced from the resistance material andcomprising exposed parts of the conductive strips separated bysaidinsulating means, the body of resistance material being constituted by alayer of materialhaving a negative temperature coefficient and a layerof material having a positive temperature coefficient, so associatedthat the "effectivetemperature coeflicient' of-the composite body is,throughout a desired range, a function of the sum of the coeflicients ofsaid layers.

References Cited in the file of this patent UNITED STATES PATENTS Re.10,944 Weston ..1...... July 17, 1888 6 Rothschild Dec. 24, 1907 RibbeApr. 20, 1909 Ruger Sept. 16, 1913 Stoekle June 24, 1930 McCreary Nov.21, 1933 Brown Aug. 14, 1956 [Moore et a1 Mar. 18, 1958

